Yep, that's about it. Too bad George didn't keep him (or other decent directors) for all the other movies he made.
And I'm not saying that episodes 4-6 were utterly fantastic movies in every way; obviously they had a good bit of camp (esp. #4), but that was part of the charm I think. They were never meant to be ultra-serious, "deep" movies with Oscar-winning performances (not that the Oscars are good indicators of performance quality these days anyway), they were meant to be visual feasts that were fun to watch while eating popcorn and watching it on a big screen. They had mildly interesting plots, decent characters, good comedic relief (thanks C3PO!), they weren't "dark" or "gritty", all in all they were great escapist entertainment, and while again not having top-of-the-line acting and script, what they had served the movies well.
That all changed with the Prequels. The plots weren't that bad and the characters might have been OK, the visuals were certainly great for the time (though too fake-looking, but lots of high-CGI movies of that era suffered the same problems), but the horrible acting and dialog really ruined it all, they broke the suspension of disbelief. (The obvious racist stereotypes in Ep.1 didn't help.) I've seen better acting on fan-made Star Trek episodes. And at least with the fan-made Star Trek stuff, you know going into it that this is what you're going to be watching. I don't expect to see amateurish acting in a $100M+ movie. And also, my expectations are much higher: I'm not forgiving of seeing a highly-paid professional actor deliver amateurish acting, while I am forgiving of an unpaid truly amateur actor deliver amateurish acting.